The present invention relates to bi-level display systems and, in particular, to adaptation of such systems for presentation of animated gray-scale images.
At the heart of a bi-level display system is a display panel typically comprising a matrix of individual, closely spaced display cells each of which resides in one of two visual states. That is, each display cell is either completely energized (on) or completely de-energized (off). Picture images and other graphic data are readily displayed on a bi-level display panel via selective energization of its cells.
Since the cells of a bi-level display panel are either completely on or completely off, the panel has no inherent capability for representing gray scale in reproduced images. Advantageously, however, it is known that a subjective impression of gray scale can be produced by way of a technique known as "dither processing." In a so-called "dithered display system" the observer is made to perceive various shades of gray, i.e., various intensities in the reproduced image by appropriate arrangement of on and off cells.
Dither is implemented in a bi-level display system by dividing the image to be reproduced into a matrix of picture elements, each element corresponding to a respective cell of the display panel. A predetermined dither threshold value is assigned to each display cell. If the intensity of any given picture element is greater than the dither threshold value assigned to the corresponding display cell, that cell is turned on. Otherwise, it is maintained off.